Generally, a manufacturing process of an optical disk comprises: a step of exposing an master disk coated with a photoresist by using an optical disk master disk recording apparatus using a laser, an electron beam and the like as a source of the exposure, and for producing an optical master disk on the surface of which protruding and recessed patterns such as information pits and grooves are formed by developing the exposed master disk; a step of producing a metal mold referred to as a stamper to which the protruding and recessed patterns are transferred from the optical master disk; a step of producing a molding substrate made of a resin by using the stamper; and a step of making a recording film, a reflective and the like formed on the molding substrate and laminated.
As an example of a master disk recording apparatus of recording patterns such as information pits and grooves of an optical disk, an electron beam recording apparatus which uses an electron beam as a recording beam is shown in FIG. 17.
The electron beam recording apparatus has at least a structure in which an electronic column 203 constituted with an electron beam source 201 for generating an electron beam, and with an electro-optical system 202 for focusing the emitted electron beam on a resist master disk 210 so as to record an information pattern on the resist master disk 210 in accordance with an inputted information signal, is provided in a vacuum vessel 213.
The electron beam source 201 which has a filament for emitting electrons by carrying a current, electrodes for confining the emitted electrons, electrodes of extracting and accelerating an electron beam, and the like, is capable of emitting the electrons from one point.
The electro-optical system 202 has a lens 204 for focusing the electron beam, an aperture 205 of determining the beam diameter of the electron beam, electrodes 206, 207 for deflecting the electron beam in accordance with an inputted information signal, a shielding plate 208 for shielding the electron beam deflected by the electrode 206, and a lens 209 for focusing the electron beam on the surface of the resist master disk 210.
The resist master disk 210 is held on a rotating device 211, and moved horizontally together with the rotating device 211 by a horizontally moving device 212. When the resist master disk 210 is moved horizontally as it is rotated, the electron beam can be spirally irradiated on the resist master disk 210, so that the information signal of the optical disk can be spirally recorded on the master disk.
A focus adjusting grid 214 is provided substantially at the same level as the surface of the resist master disk 210. The focus adjusting grid 214 is provided to adjust the focus position of the lens 209 so as to make the electron beam focused on the surface of the resist master disk 210. The electron beam is irradiated on the focus adjusting grid 214, and reflected electrons reflected by the focus adjusting grid 214 and secondary electrons emitted from the focus adjusting grid 214 are detected by a detector, so that the focus position of the lens 209 can be adjusted by the focus adjusting grid 214 on the basis of the view of the monitored grid image.
The electrode 206 is provided to deflect the electron beam to a direction substantially perpendicular to the moving direction of the horizontally moving device 212. The electrode 206 deflects the electron beam toward the shielding plate 208 in accordance with a signal inputted to the electrode 206, so that it is possible to select whether the electron beam is irradiated on the resist master disk 210 or not, and to thereby record an information pit pattern and the like on the resist master disk 210.
The electrode 207 is provided to deflect the electron beam in a direction substantially perpendicular to the electrode 206, and is capable of deflecting the electron beam in a direction substantially the same as the moving direction of the horizontally moving device 212 in accordance with a signal inputted to the electrode 207. The moving direction of the horizontally moving device 212 corresponds to the radial direction of the resist master disk 210 to be recorded, and it is possible to correct a fluctuation of the track pitch of the optical disk, and the like, by the signal inputted to the electrode 207.
The horizontally moving device 212 includes, for example, a screw feed type as shown in FIG. 18, in which a screw 301 is rotated by a motor 302 so as to make a resist master disk 303 linearly fed by a screw pitch provided for a stage 304 holding the resist master disk 303, or a swing arm type as shown in FIG. 19, in which a resist master disk 402 is fed with curvature by an arm 403 as the resist master disk 402 is rotated about one point 401. A length measuring apparatus, such as a laser interference length measuring meter, is mainly used as a position detecting device of the horizontally moving device 212, which is used to improve the feeding accuracy of the horizontally moving device 212, and the like. In the horizontally moving device 212 having a linear feeding structure, as shown in FIG. 18, a laser beam is irradiated by the laser interference length measuring meter and the like from the outside to a target provided on the horizontally moving device 212, and the position of the horizontally moving device 212 is measured from an interference pattern and the like, formed by reflected light beams reflected from the target, and the like, whereby the deviation amount from a desired position is detected. As a result, it is possible to drive the horizontally moving device 212 so as to correct the detected deviation, or to drive the electrode 207 and the like to control the irradiation position of the electron beam (Japanese Patent Laid-Open No. 2002-141012).
In the horizontally moving device 212 of the swing arm type as shown in FIG. 19, unlike the case of linear feeding, it is difficult to use the laser interference length measuring meter and the like, because of the characteristic that the position measuring point is moved with curvature. In the case where an optical disk having an information density approximately equal to a CD and a DVD is produced, the allowable value of fluctuation amount of the track pitch of the optical disk is large. Thus, even when the horizontally moving device 212 such as of the swing arm type which moves with curvature is used, the recording operation can be performed with sufficient accuracy only by monitoring the precision of a motor of driving the arm and the output of an encoder and the like provided for the rotating shaft of the motor, without using a length measuring apparatus such as a laser interferometer.
However, in a next generation optical disk storing a large volume of information such as digital High Vision information, the track pitch is reduced to roughly a half in comparison with the DVD, and the allowable value of fluctuation amount of the track pitch is also significantly reduced. For this reason, it is necessary to introduce a system capable of performing accurate position detection and position control by servo, even in the horizontally moving device 212 such as of the swing arm type which moves with curvature.
That is, in the case of the swing arm type, the electron beam is moved along a path shown by a dotted line in FIG. 19 in association with the movement of the horizontally moving device 212. The path has a circular arc shape centered on the point 401, which causes a deviation from a straight line in the radial direction of the resist master disk 402. As the deviation is increased, the deviation of the track pitch is also increased. In producing the large capacity next generation optical disk as described above, the deviation of the track pitch becomes a problem. For example, in the example shown in FIG. 19, the track pitch of the peripheral edge part of the resist master disk 402 is narrower than that of the center part.
Further, in the region where the track pitch is narrowed, the track pitch may be fluctuated by vibration and the like. Such fluctuation of the track pitch also becomes a problem in producing the large capacity next generation optical disk.
FIG. 20 shows a cross-section of the electron beam recording apparatus provided with the horizontally moving device 212 of the screw feed type shown in FIG. 18. The position of the horizontally moving device 212 can be corrected with respect to a portion for fixing a laser interference length measuring meter 305 (for example, in the case of the electron beam recording apparatus, a bottom surface 306 of the vacuum vessel, to which the base of the horizontally moving device 212 is fixed). However, in practice, there may be a case where the relative positional relationship between the recording beam focusing device for focusing the recording beam (for example, the electronic column in the case of the electron beam recording apparatus) and the horizontally moving device 212 can not be sufficiently corrected. In this case, such correction is not enough to improve the feeding accuracy of the spiral pattern of the optical disk and the like which is formed by irradiating the recording beam on the resist master disk 210.